Image pickup apparatuses such as video cameras, digital video cameras or still video cameras having image pickup devices such as CCDs (Charge Couple Devices) are widely and generally used.
Image pickup devices such as CCDs are narrow in dynamic range compared to silver halide cameras. For this reason, when an image is taken against backlight with such an image pickup device, lost highlight detail which causes a bright section to lose grayscale or lost shadow detail which causes a dark section to lose grayscale occur in a reproduced image.
In a conventional type of image pickup apparatus, the amount of exposure is adjusted to become correct for a subject, by an automatic exposure function, but there still remain many cases where although a main section of a subject has correct exposure, lost highlight detail and the like occurs in a background and the like.
In addition, in the conventional type of image pickup apparatus, back compensation has been performed in such a manner that the reproducibility of an image at a low luminance signal level/a middle luminance signal level (a low-middle luminance signal level) is weighted while the detail of a high luminance section is lost. However, there are also cases where lost highlight details in a background desire to be made visible.
For this reason, in order to cope with an image of wide dynamic range containing a bright section and a dark section as mentioned above, there has been provided an image pickup apparatus (wide dynamic range camera) capable of taking an image of wide dynamic range by synthesizing an image whose main subject is a comparatively bright section captured by a high speed shutter or the like and an image whose main subject is a comparatively dark section captured by a low speed shutter or the like.
However, in the above-mentioned image pickup apparatus capable of taking an image of wide dynamic range, such as a wide dynamic range camera, the proportion in which the dynamic range of an output image reproducible as a video signal is assigned to a high luminance section in which the luminance signal levels correspond to high luminance and to a low-middle luminance section in which the luminance signal levels correspond to low luminance/middle luminance is constantly fixed irrespective of the kind of subject.
Accordingly, for example, if an image signal of the high luminance section is absent in the output image, an image signal assigned to the high luminance section in the dynamic range of the output image is absent, while the remaining low-middle luminance section only is assigned to the dynamic range. This hinders effective use of the dynamic range and provides a generally dark image.
The present invention has been conceived in view of the above-mentioned problems, and an object of the present invention is to provide a novel and improved image pickup apparatus capable of performing dynamic assignment in the dynamic range of an output image according to the kind of subject.